Power Over Ethernet Powered Device Having Automatic Power Signature

1. An interface circuit for a Powered Device (PD) that is couplable to a Power Sourcing Equipment (PSE) in a Power over Ethernet (PoE) system, the interface circuit comprising: a comparator coupled to a first resistor through which current flows from the PSE when connected to a load within the PD, the comparator configured to measure a voltage drop across the first resistor to determine the load current and generate an output signal representative of the load current; a timing logic responsive to the output signal for generating switch control signals and an enable signal; a switch responsive to one of the switch control signals for inserting a second resistor in a current path of the first resistor for generating an accurate current pulse in order to meet Maintaining Power Signature (MPS) requirements; and an error amplifier coupled to the current path and responsive to the enable signal for automatically generating a load pulse of sufficient magnitude that, along with current drawn by the PD to power a load, indicates to the PSE that power to the PD is being maintained.

2. The interface circuit of claim 1 further comprising a first transistor coupled in series with the first resistor and having a gate coupled to a current limiting circuit for limiting current to the load; a second transistor coupled in series with the second resistor; and wherein the switch disables the first transistor and couples a gate of the second transistor to the current limiting circuit.

3. The interface circuit of claim 1 , wherein the interface circuit provides power to a general LED lighting.

4. The interface circuit of claim 1 , wherein the load pulses have a predetermined duration and spacing.

5. The interface circuit of claim 1 , wherein the first resistor is a low valued shunt and the second resistor has a resistance of at least an order of a magnitude higher than the first resistor.

6. An interface circuit for a Powered Device (PD) for a Power over Ethernet (PoE) system, the interface circuit comprising: a comparator for measuring a load current in the PD and comparing the load current to a reference and generating an output signal; a timing logic circuit responsive to the output signal for generating an enable signal; an error amplifier responsive to the enable signal for generating an output voltage based on a reference; and a resistor coupled to an output of the error amplifier for drawing a current pulse when the PD is coupled to a Power Sourcing Equipment (PSE) to automatically indicate to the PSE, that the PSE is to maintain power delivery to the PD.

7. The interface circuit of claim 6 , wherein the magnitude of the load pulses are controlled by an external resistor.

8. The interface circuit of claim 6 , wherein the interface circuit provides power to a general LED lighting.